Method of forming a controlled and uniform lightly phosphorous doped silicon film

ABSTRACT

Method of forming a lightly phosphorous doped silicon film. A substrate is provided. A process gas comprising a phosphorous source gas and a disilane gas is used to form a lightly phosphorous doped silicon film on the substrate. The diluted phosphorous source gas has a phosphorous concentration of 1%. The phosphorous source gas and the disilane gas have a flow ratio less than 1:100. The lightly phosphorous doped silicon film has a phosphorous doping concentration less than 1×10 20  atoms/cm 3 .

BACKGROUND OF THE INVENTION

[0001] 1). Field of the Invention

[0002] This invention relates generally to a semiconductor processingmethod, and more specifically to the manufacture of a lightlyphosphorous doped silicon film that can be incorporated into asemiconductor device.

[0003] 2). Discussion of Related Art

[0004] Integrated circuits are usually manufactured in and on siliconand other semiconductor substrates or wafers. Most often, silicon isused as the substrate for these integrated circuits. Silicon is alsooften used to fabricate the associated circuit elements. Circuitelements such as transistor gate electrodes, transistor gatedielectrics, and capacitor electrodes are made out of silicon. Forexample, a transistor typically has a gate dielectric film and a gateelectrode, which is formed on the gate dielectric film, which is formedon a silicon substrate. The gate electrode is doped with a dopant suchas boron, phosphorus, or arsenic. The substrate is subsequently heatedto activate the dopant and make the electrode conductive.

[0005] Doping the circuit elements after the formation step increasescost. Insitu doping such as insitu phosphorous doped silicon films havebeen used in the making of many circuit elements, for example, in makinggate electrodes, silicide stacks and floating gates. Insitu dopingindicates that the films (or silicon films) are doped as they are beingformed in the same process and in the same deposition chamber.Conventionally, silane or monosilane (SiH₄) is normally used as asilicon source and phosphine (PH₃) is used as dopant source for theinsitu deposition of the phosphorous-doped silicon film.

[0006] In one embodiment, the fabrication of a phosphorous-doped siliconfilm is carried out in a conventional batch type chemical vapordeposition system. Such a system typically involves a hot wall furnacesystem, which includes a resistance furnace, a quartz reactor tube, somegas inlets, and a wafer boat that allows for processing of multiplewafers at the same time. Typically, multiple silicon wafers arevertically positioned upon the wafer boat for deposition. The wafers areradiantly heated by resistive heating coils surrounding the tube.Reactant gases are metered into one end of the tube (through some gasinlets using a mass flow controller). Reaction by-products are pumpedout the other end of the tube (e.g., via an exhaust pump). Fabricationin batch limits the ability of varying the dopant concentration betweenwafers. It is also much more difficult to customize the film formingprocess for particular applications. Additionally, if anything goeswrong during the deposition process, a large batch of substrates aredamaged and rendered useless.

[0007] One disadvantage of the conventional methods of insitu doping isthat it is difficult to control dopant concentration especially informing the lightly doped film. Another disadvantage is that the lightlydoped film is not uniform.

[0008] Some current methods have used disilane (Si₂H₆) as the siliconsource and phosphine (PH₃) as the dopant source for the insitudeposition of the phosphorous-doped silicon film in a single-waferdeposition chamber. See for example, U.S. Pat. Nos. 5,607,724 and5,614,257, assigned to Applied Materials, Inc. These methods did notdiscuss the non-uniform problem for the phosphorous doping concentrationin a lightly-doped silicon film.

SUMMARY OF THE INVENTION

[0009] According to an aspect of the invention, an insitu lightlyphosphorous doped silicon film is formed in a single-wafer depositionchamber using disilane and phosphine as reactant gases.

[0010] A substrate is provided. A process gas comprising a phosphoroussource gas and a disilane gas is used to form a lightly phosphorousdoped silicon film on the substrate. The diluted phosphorous source gashas a phosphorous concentration of 1%. The phosphorous source gas andthe disilane gas have a flow ratio less than 1:100. The lightlyphosphorous doped silicon film has a phosphorous doping concentrationless than 1×10²⁰ atoms/cm³.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The present invention is further described by way of exampleswith reference to the accompanying drawings, wherein:

[0012]FIG. 1 illustrates a cross-sectional side view of an exemplarysemiconductor processing system that is used for carrying outembodiments of the present invention;

[0013]FIG. 2 illustrates an enlarged view of an exemplary chamber andinternal components of the chamber;

[0014]FIGS. 3A to 3H illustrate cross-sectional side views of asemiconductor device that can be formed using some of the exemplaryembodiments of the present invention;

[0015]FIG. 4 illustrates an exemplary method of fabricating a dopedsilicon comprising film wherein disilane and phosphine are used asreactant gases; and

[0016]FIG. 5 illustrates a comparison of flow ratio effect betweenmonosilane/phosphine and disilane/phosphine. In this figure, thephosphine is diluted to 1% phosphine in hydrogen (H₂) gas.

[0017]FIG. 6 illustrates cluster tool that can be used for some of theembodiments of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0018] The present invention includes a novel method of forming alightly phosphorous doped comprising film in a single-wafer depositionchamber using a disilane (Si₂H₆) source gas and a phosphorous source gassuch as phosphine (PH₃). In the following description, for purposes ofexplanation, numerous specific details are set forth in order to providea thorough understanding of the present invention. It will be evident,however, to one skilled in the art that the present invention may bepracticed without these specific details. In other instances, specificapparatus structures and methods have not been described so as not toobscure the present invention. The following description and drawingsare illustrative of the invention and are not to be construed aslimiting the invention.

[0019] This discussion relates to forming a lightly phosphorous dopedsilicon film. The lightly phosphorous doped silicon film can be amonocrystalline, a polycrystalline film, or an amorphous film.Additionally, the lightly phosphorous doped silicon film may includeother silicon comprising film that can be doped with phosphorous, forexample, silicon germanium.

[0020] In one embodiment, a lightly phosphorous dopes silicon film isformed on a substrate. The lightly phosphorous dopes silicon film isformed under a process pressure between 30 Torr and 350 Torr and aprocess temperature between 500° C. and 650° C. A process gas mixturecomprising a disilane gas and a phosphorous source gas is used to formthe lightly phosphorous dopes silicon film. In one embodiment, thephosphorous source gas is a diluted phosphorous source gas containing 1%phosphorous and 99% hydrogen (H₂) gas. In this example, the 1% dilutedphosphorous source gas and the disilane gas have a flow ratio between1:10 to 15:10. In an embodiment where the phosphorous source gas is notdiluted, the phosphorous source gas and the disilane gas have a flowratio less than 1:100. In one embodiment, the disilane gas and thephosphorous source gas are thermally decomposed to form the lightlyphosphorous doped silicon film.

[0021] The lightly phosphorous doped silicon film formed in accordancewith the present invention has a phosphorous doping concentration lessthan 1×10²⁰ atoms/cm³. The lightly phosphorous doped silicon film isalso uniform or substantially uniform. The phosphorous dopingconcentration across the substrate is also uniform. The lightlyphosphorous doped silicon film has a low dopant concentration yet, ahigher amount of the phosphorous source gas can be used. When theprocess gas mixture includes a disilane gas, the amount of thephosphorous source gas that can be used to form the lightly phosphorousdopes silicon film is about one (1) magnitude higher than typicallyrequired when the process gas mixture includes mono silane. This isparticularly useful for forming the film with lightly phosphorous dopeddopant since being able to use more phosphorous source gas makes iteasier to control the flow rate of the phosphorous source gas. Thedoping concentration is thus much easier to control, and the dopant inthe film is much more uniform.

[0022] In one embodiment, a single wafer deposition chamber is used toform the lightly phosphorous doped silicon film. An example of such asingle wafer deposition chamber is described below (See FIG. 1).

[0023]FIG. 1 illustrates an exemplary semiconductor processing system 10that is used for carrying out the exemplary methods of the presentinvention (see below). The system 10 includes a low-pressure chemicalvapor deposition chamber 12, a gas supply apparatus 14, a susceptor 16,and a susceptor elevating apparatus 18.

[0024] The chamber 12 is a single-wafer deposition chamber. The chamber12 is also a resistively heated single wafer deposition chamber. Thechamber 12 can also be a cold-wall chamber in which a coolant fluid issupplied to a container (not shown) surrounding the wall of the chamber12 to prevent the chamber 12 from getting too hot. With the reactantgases and the temperature in the range of 500° C. or 650° C. or evenhigher, being processed in the chamber 12, the chamber 12 may be easilycorroded unless made out of a corrosion resistant material, which isoften expensive. With the cold-wall feature, the chamber 12 does notneed to be made out of such an expensive material that is corrosionresistant. The chamber 12 can be made out of an aluminum alloy or othersuitable metal.

[0025] The chamber 12 includes a lower body 20 and a lid 22. The lid 22seals peripherally with an upper extremity of the body 20. The body 20and the lid 22 jointly define an inner volume 24 of approximately fiveto seven liters. A first gas inlet port 26 is formed through a center ofthe lid 22. A second gas inlet port 28 is formed into a base of thesusceptor elevating apparatus 18 and leading directly into the bottomside of the chamber 12. A gas outlet port 30 is formed in a side of thebody 20. The body 20 also has a slit valve opening 32 in one sidethereof, and a susceptor elevating apparatus opening 34 in a basethereof.

[0026] A gas dispersion plate 38 or “shower head” is mounted below thelid 22. Surfaces of the lid 22 and the gas dispersion plate 38 jointlydefine a thin horizontal cavity 40. The gas dispersion plate 38 has amultitude of openings (not shown) formed therethrough that place thecavity 40 in communication with the inner volume 24.

[0027] A gas accumulation ring (or “pumping plate”) 42 is mounted withinthe chamber 12. The gas accumulation ring 42 and the surfaces of thechamber 12, define a ring volume 44. Gas outlet openings 46 are formedas an open gate between the pumping plate 42 and the dispersion plate38. The ring volume 44 is in communication with the gas outlet port 30.

[0028] A process gas or gases can flow through the first gas inlet port26 into the cavity 40. In one embodiment, the process gas or gasesinclude a process gas mixture containing a disilane gas and aphosphorous source gas to form the lightly phosphorous dopes siliconfilm. The process gas or gases may also include other type of gasmixtures that will deposit other films on a substrate or otherwise treator clean the substrate or clean the chamber 12. Gas then flows radiallywithin the cavity 40. The gas or gases can then flow through theopenings in the gas dispersion plate 38 into the inner volume 24. Moreprocess gas can enter through the second gas inlet port 28 into theinner volume 24. Typically, only a purging gas or an inert gas such asnitrogen (N₂) gas is introduced to the inlet port 28. The reactant gasesare introduced through the inlet port 26. Introducing the inert gasthrough the inlet port 28 during the film deposition process preventsundesirable deposition on the bottom side of the chamber 12. The processgas or gases can exit the inner volume 24 through the gas outletopenings 46, be accumulated in the ring volume 44, and subsequently bepumped out through the gas outlet port 30.

[0029] Referring to FIG. 2, the elevating apparatus 18 includes a set ofelevating pins 48, a pin elevator 50, and a susceptor elevator 52. Thepin elevator 50 and the susceptor elevator 52 are tubular members thatextend through the apparatus opening 34 into the inner volume 24. Thesusceptor elevator 52 is, for the most part, located within the pinelevator 50. A portion of the susceptor elevator 52 extends out of anupper end of the pin elevator 50. A susceptor 16 is mounted to an upperend of the susceptor elevator 52. The susceptor is used to support asubstrate 79 (shown in outline form in FIGS. 1 and 2). Vertical movementof the susceptor elevator 52 causes vertical movement of the susceptor16.

[0030] The pins 48 extend through openings (not shown) in the susceptor16. Each pin 48 has a head 56 at an upper end thereof. The pin elevator50 engages with lower ends of the pins 48. Vertical movement of the pinelevator 50 causes vertical movement of the pins 48 relative to thechamber 12. The pins 48 also move relative to the susceptor 16, assumingthat the susceptor 16 is stationary.

[0031] Referring again to FIG. 1, the gas supply apparatus 14 includes agas bank 60 and a gas-mixing manifold 62. The gas supply apparatus 14further couples to a processor/controller 64, and memory 66. The gasbank 60 has number of different gas sources. In one embodiment, the gassources include nitrogen gas (N₂), disilane (Si₂H₆) gas, and aphosphorous source gas such as a phosphine (PH₃) gas. In anotherembodiment, other carrier/dilution gases such as helium (He) gas,hydrogen (H₂) gas, nitrogen (N₂) gas, xenon (Xe) gas, and argon (Ar)gas, can be included in the gas sources. Each of the gas sources isconnected through a respective valve (not shown) to the gas-mixingmanifold 62. The gas-mixing manifold 62 is connected to the first gasinlet port 26. In one embodiment, an inert gas such as an N₂ gas is alsoconnected through a valve (not shown) to the second gas inlet port 28.

[0032] In one embodiment, the processor/controller 64 controlsoperations of the gas bank 60. The processor/controller 64 is connectedto the valves through which the gases can exit the gas bank 60 and enterthe chamber 12. The processor/controller 64 can operate each valveindependently so as to open or close flow from a respective gas sourceto either the gas-mixing manifold 62 or to the second gas inlet port 28.The memory 66 is connected to the processor/controller 64. A program ora set of instructions stored in the memory 66 and read by theprocessor/controller 64 can be used to control the operations of the gasbank 60. The valves can thus be opened or closed according to theinstructions stored in the memory 66.

[0033] In one embodiment, the processor/controller 64 also controlsoperations of the semiconductor processing system 10. For example, theprocessor/controller 64 executes a program stored in the memory 66wherein the program further controls the process temperature (e.g.,between 500-650° C.), process pressure (e.g., between 30-350 Torr), andthe loading and unloading of a substrate into the chamber 12. In oneembodiment, the program controls the dilution of the phosphorous sourcegas to be between 0.1% and 10%. In yet another embodiment, the programcontrols a flow ratio for the diluted phosphorous source gas and thedisilane gas (e.g., a flow ratio of 1:10 to 15:10 of a 1% dilutedphosphorous source gas to the disilane gas).

[0034] Referring to FIG. 2, when in use, a substrate 79 is located on atransfer blade 70 and then be transported on the transfer blade 70through the slit valve opening 32 into the inner volume 24 of thechamber 12. The substrate 79 can be inserted into the chamber 12 using arobot assembly.

[0035] To load a substrate (e.g., the substrate 79), the pin elevator 50is raised so that the heads 56 make contact with a lower surface of thesubstrate, and lifts the substrate off the blade 70. The transfer blade70 is then removed through the slit valve opening 32. The susceptor 16remains stationary throughout this process. With the pin elevator 50remaining stationary, the susceptor elevator 52 is then raised. Raisingof the susceptor elevator 52 causes movement of the susceptor 16 in avertically upward direction, while the pins 48 slide along the openingsin the susceptor 16. The susceptor 16 is raised until an upper surface72 of the susceptor 16 makes contact with a lower surface of thesubstrate. The susceptor 16 is then further elevated until an uppersurface of the substrate is at a required distance from the gasdispersion plate 38. In one embodiment, the upper surface of thesubstrate is at a distance of approximately 14 mm from the gasdispersion plate 38.

[0036] In one embodiment, a current is provided to a resistive heater 76(see FIG. 2) located within the susceptor 16. In one embodiment, thesusceptor 16 can be made out of ceramic, graphite, aluminum, or othersuitable material, preferably, ceramic. The current heats the resistiveheater 76, and the heat conducts from the resistive heater 76 throughthe susceptor 16 to a substrate. In one embodiment, a thermocouple 78(see FIG. 2) is located within the susceptor 16, and providestemperature feedback for purposes of controlling the temperature of thesusceptor 16 and, indirectly, the temperature of the substrate. In oneembodiment, the temperature of the substrate is approximately 20° C.lower than the temperature measured at the susceptor 16.

[0037] In one embodiment, the chamber 12 has a reacting space 47. Thereacting space 47 is the area between the dispersion plate 38 and thesusceptor 16. In one embodiment, the reacting space 47 has a volume ofabout 750 cm³, which is the dispersion plate area times the distancebetween the dispersion plate 38 and the susceptor 16. In anotherembodiment, the chamber 12 has an inner volume 24 of about 5 to 7litters.

[0038] FIGS. 3A-3H illustrate an exemplary process of making asemiconductor device such as a FLASH memory, a capacitor, or atransistor in accordance with the embodiments of the present invention.FIG. 3A illustrates a cross-sectional portion of a substrate 102 whereupon a device can be formed. In one embodiment, the substrate 102 ismade out of monocrystalline silicon. In one embodiment, the substrate102 is a silicon wafer. The substrate 102 may include a thin film ofepitaxial silicon.

[0039] A thin silicon dioxide insulation film 104 (e.g., a gatedielectric film) is formed on an upper surface of the substrate 102 asillustrated at FIG. 3B. In an embodiment where the substrate 102includes the epitaxial silicon film, the insulation film 104 is formedon the epitaxial silicon film. The insulation film 104 is typically lessthan 25 Å thick. In one embodiment, the insulation film 104 is formed tocontain may be made of silicon dioxide, nitrided silicon dioxide, oranother dielectric material such as a high-k material. In oneembodiment, to form the insulation film 104, conventional method such asthermal oxidation can be used.

[0040] Next, a lightly phosphorous doped silicon film 106 is formeddirectly on the exposed upper surface of the insulation film 104 asillustrated in FIG. 3C. In one embodiment, the lightly phosphorous dopedsilicon film 106 is a floating gate of a FLASH memory device. In oneembodiment, an exemplary method 400 is used to form the lightlyphosphorous doped silicon film 106. The method 400 is illustrated inillustrated in FIG. 4.

[0041] In one embodiment, the substrate 102 is placed in the chamber 12described above. In one embodiment, the substrate 102 is positioned atapproximately 13 mm from the gas dispersion plate 38 as hereinbeforedescribed. A process temperature and a process pressure are obtained atoperation 402. In one embodiment, the process pressure is between 30Torr and 350 Torr. The process temperature is between 480° C. and 630°C.

[0042] Next, an inert gas such as an N₂ gas is introduced into thechamber 12 at operation 404 to equilibrate the chamber 12. The N₂ gas isintroduced through the inlet ports 26 and 28. Through the gas inlet port26, the N₂ gas is introduced into the top of the chamber 12 and in oneembodiment, with a flow rate of approximately 6000 standard cubiccentimeters per minute (sccm). Through the gas inlet port 28, the N₂ gasis introduced into the bottom of the chamber 12 and in one embodiment,with a flow rate of approximately 2000 sccm. In one embodiment, the flowrates for the N₂ gas flows through the inlet port 26 and 28 may a rangefrom about 2000 sccm to about 10,000 sccm.

[0043] At operation 406, a disilane gas and a phosphorous source gas(e.g., phosphine (PH₃) gas) are simultaneously introduced into thechamber 12. In one embodiment, the disilane gas is pure (not diluted)and is introduced into the chamber 12 at a relative flow rate rangingfrom 20 sccm to 200 sccm, and ideally, 60 sccm. The flow rate of thedisilane gas can be varied depending on the size of the chamber 12. Inone embodiment, the flow rate of the disilane gas is selected for thechamber 12 that has the inner volume 24 with a volume between 5-7litters and the reacting space 47 of about 750 cm³. Additionally, therelative flow rate of the disilane gas can be varied depending on thedesired thickness of the film. Generally, the relative flow rate of thedisilane gas is higher for a thicker film than for a thinner film.

[0044] In on embodiment, the phosphorous source gas is diluted with adilution/carrier gas, which is an inert gas such as hydrogen (H₂) gas toform a diluted phosphorous source gas. When the phosphorous source gasis PH₃, the diluted phosphorous source gas is a diluted PH₃ gas. Otherinert gases that can be used to dilute the phosphorous source gas mayinclude an N₂, an Ar gas, and a Xe gas. In one embodiment, the dilutedphosphorous source gas contains approximately 1.0% of the phosphoroussource gas and approximately 99% of the hydrogen gas. In anotherembodiment, the diluted phosphorous source gas contains anywhere from0.10% to 10% of the phosphorous source gas. The relative flow rate forthe diluted phosphorous source gas is between 20 sccm and 300 sccm, andideally, 90 sccm. In one embodiment, the flow rate of the dilutedphosphorous source gas is selected for the chamber 12 that has the innervolume 24 with a volume between 5-7 litters and the reacting space 47 ofabout 750 cm³.

[0045] In another embodiment, the relative flow rate of the dilutedphosphorous source gas can be adjusted according to the concentration ofthe phosphorous in the diluted phosphorous source gas. When thephosphorous source gas is the pure (or undiluted) phosphorous sourcegas, the relative flow rate of this phosphorous source gas is small inorder to achieve a particular desired phosphorous doping concentration.When the phosphorous source gas is diluted, the relative flow rate forthe diluted phosphorous source gas is higher than that for the undilutedphosphorous source gas to achieve the particular desired phosphorousdoping concentration.

[0046] For instance, to form a lightly phosphorous doped silicon film,(e.g., with a dopant concentration less than 1×10²⁰ atoms/cm³, therelative flow rate for the pure or undiluted phosphorous source gas hasto be much less than 1-2 sccm for the chamber 12 with the inner volume24 volume between 5-7 litters and the reacting space 47 of about 750cm³. Controlling or metering such a low flow rate into the chamber 12 isextremely difficult and often results in non-uniformity of thephosphorous dopant in the final film. In another embodiment, thephosphorous source gas is the diluted phosphorous source gas in therange of 0.1% to 10% as mentioned above. Since it is easier to controlthe relative flow rate of a more diluted phosphorous source gas than theless diluted phosphorous source gas, it is preferred that thephosphorous source gas be as diluted as possible.

[0047] It is to be appreciated that the flow rate of disilane gas, thephosphorous source gas, the diluted phosphorous source gas, the inertgas, or any other gases that are introduced into the chamber 12 isrelative to the volume of the chamber 12.

[0048] At operation 408, the disilane and the phosphorous source gasesare thermally decomposed to form the lightly phosphorous doped siliconfilm 106. Once a sufficiently thick lightly phosphorous doped siliconfilm 106 is deposited, the disilane and the phosphine gases are shut offas illustrated at operation 410. In one embodiment, the lightlyphosphorous doped silicon film 106 that is formed is a polysilicon film.In one embodiment, the deposition of the lightly phosphorous dopedsilicon film 106 is continued for approximately 45 seconds, so that thelightly phosphorous doped silicon film 106 is approximately 2000 Åthick. The time for deposition may be varied according to the desiredthickness for the lightly phosphorous doped silicon film 106. In anotherembodiment, the lightly phosphorous doped silicon film 106 may bebetween 500 Å and 2000 Å thick.

[0049] In one embodiment, the chamber 12 is purged with an inert gassuch as an N₂ gas as illustrated at operation 412.

[0050] One advantage of using the disilane gas in forming the lightlyphosphorous doped silicon film 106 is that more of the phosphoroussource gas or the diluted phosphorous source gas can be used. It iseasier to form the lightly phosphorous doped silicon film with aphosphorous doping concentration less than 1×10²⁰ atoms/cm³.

[0051] Disilane has a faster reaction rate than monosilane. The siliconatoms in the disilane thus incorporate into the film at a faster ratethan in the case of monosilane. The deposition rate is thus faster. Inorder to allow the phosphorous atoms in the phosphorous source gas to beincorporated into the film, more of the phosphorous source gas isrequired. The increased amount of the phosphorous source gas leads tothe need for a higher relative flow rate for the phosphorous source gas.In one embodiment, requiring more phosphorous source gas makes it easierto control the relative flow rate of the phosphorous source gas that isintroduced into the chamber 12. In one embodiment, when disilane isused, the phosphorous source gas needed is at least one order ofmagnitude greater than when monosilane is used to achieve the samephosphorous doping concentration in the doped film (see FIG. 5discussion). The ability to use more phosphorous source gas in the filmdeposition process thus gives a better and more accurate control ofuniformity of the phosphorous doping concentration in the final film.

[0052] Furthermore, when higher phosphorous amount is needed, the filmdeposition process is not sensitive to and/or impacted a small deviationin the amount of the phosphorous source gas or the diluted phosphoroussource gas that is used. In one embodiment, when more of the amount ofthe phosphorous is used, the impact by the out-gassing experiences bythe film being formed in the chamber 12 is much smaller. Out-gassingoccurs when some of the phosphorous atoms from the phosphorous sourcegas or the diluted phosphorous source gas that got absorbed to thesurfaces inside the chamber 12, for example, during the initializationprocess or due to other factors, get released or desorbed from thesurfaces. These phosphorous atoms may incorporate themselves into thefilm that is being formed. The impact by the out-gassing is minimizedwhen more of the phosphorous source gas or the diluted phosphoroussource gas can be introduced into the chamber 12.

[0053] When monosilane is used, it is difficult to control the relativeflow rate of the phosphorous source gas or the diluted phosphoroussource gas, which needs to be very small. Hence, it is much moredifficult to control or obtain the desirable concentration of thephosphorous doping concentration in the final film. Lacking the abilityto control the phosphine doping concentration, the film dopant is lessuniform. It is also much more difficult to repeat the dopantconcentration across the substrate. The non-uniform dopant concentrationobserved from substrate to substrate, or wafer to wafer, becomes abigger problem when a single-wafer deposition chamber is used to formthe lightly phosphorous doped silicon film.

[0054]FIG. 5 illustrates in more details the impact of the flow ratio ofthe disilane gas and the phosphorous source gas on the phosphorousdoping concentration. In one embodiment, the flow ratio of thephosphorous source gas and disilane gas in the chamber 12 determines thephosphorous doping concentration on a film. FIG. 5 further illustratesthe different in flow ratio requirements when monosilane is used versuswhen disilane is used to form a film that is doped with phosphorous.

[0055] In one embodiment, FIG. 5 pertains to the impact of the flowratio of the phosphorous source gas and the disilane gas wherein thephosphorous source gas is a 1% diluted phosphorous source gas (1%phosphorous and 99% H₂ gas). The discussion herein of FIG. 5 issimilarly applied to the case where the phosphorous source gas is pureor undiluted. The axis 502 indicates the flow ratio of the 1% dilutedphosphorous source gas and the disilane (Si₂H₆) gas. The axis 502 alsoindicates the flow ratio of the 1% diluted phosphorous source gas andthe monosilane (SiH₄) gas. The axis 504 indicates the concentration(atoms/cm³) of the phosphorous dopant in the film (e.g., a phosphorousdoped silicon film) that is formed using these gases.

[0056] In one embodiment, when the monosilane gas is used, to form afilm with a phosphorous doping concentration of 1×10²⁰ atoms/cm³, theflow ratio for the 1% diluted phosphorous source gas and the monosilanegas is 1:10 (or 0.1). When the disilane gas is used, to form a film witha phosphorous doping concentration of 1×10²⁰ atoms/cm³, the flow ratiofor the 1% diluted phosphorous source gas and the disilane gas is 1:1(or 1). In another embodiment, when the monosilane gas is used, to forma film with a phosphorous doping concentration of less than 1×10²⁰atoms/cm³, for instance, a phosphorous doping concentration “X”, theflow ratio for the 1% diluted phosphorous source gas and the monosilanegas is 3.5:100 (or 0.035). When the disilane gas is used, to form a filmwith the same phosphorous doping concentration “X”, the flow ratio forthe 1% diluted phosphorous source gas and the disilane gas is 4:10 (or0.4).

[0057] Alternatively, for the same amount of phosphorous source gas,when monosilane is used, the film that is formed has a higherphosphorous doping concentration than when disilane is used. Forinstance, when the flow ratio of the 1% diluted phosphorous source gasand the disilane gas is 1:1 (or 1), the film formed has a phosphorousdoping concentration of slightly less than 1×10²⁰ atoms/cm³. On theother hand, when the flow ratio of the 1% diluted phosphorous source gasand the monosilane gas is 1:1 (or 1), the film formed has a phosphorousdoping concentration of nearly 1×10²¹ atoms/cm³, which is almost anorder of magnitude greater than when disilane is used.

[0058] As can be seen, FIG. 5 illustrates that in order to reach thesame phosphorous doping concentration, the flow ratio of the 1% dilutedphosphorous source gas and the disilane gas is about one (1) order ofmagnitude greater than that of the 1% diluted phosphorous source gas andthe monosilane gas. In other words, more phosphorous is needed to reacha desired phosphorous doping concentration in the case of disilane thanin the case of monosilane. Controlling a greater amount of phosphorous,especially when making the lightly doped films (dopant concentrationless than 1×10²⁰ atoms/cm³). Furthermore, when more phosphorous isrequired, it is easier to obtain a more stable and repeatable processfrom wafer to wafer. The uniformity in film thickness is alsodramatically improved, as it is much easier to obtain controllable andrepeatable amount of phosphorous for the doping.

[0059] Following FIG. 3C, a control oxide film 108 is formed as shown inFIG. 3D. The control oxide film 108 is a dielectric film that is formedover the lightly phosphorous doped silicon film 106. In one embodiment,the control oxide film 108 is a silicon dioxide film formed usingconventional methods.

[0060] Alternatively, the control oxide film 108 can be formed in thesame chamber 12 immediately following the formation of the lightlyphosphorous doped silicon film 106 described above. In one embodiment,to form the oxide film 108 immediately after the lightly phosphorousdoped silicon film 106 is formed, the phosphorous source gas flow isshut off while the disilane gas flow is continued. An oxidation sourcegas (e.g., nitrous oxide (NO₂) and ozone (O₃)) is introduced into thechamber 12. The disilane gas and the oxidation source gas are decomposedto form the control oxide film 108.

[0061] In another embodiment, immediately following the forming of thelightly phosphorous doped silicon film 106, both the disilane gas andthe phosphorous source gas flows are shut off. Another silicon sourcegas such as monosilane is introduced into the chamber 12 together withthe oxidation source gas to form the control oxide film 108. Althoughdisilane gas is not the only silicon source gas that can be used to formthe control oxide film 108, it may be convenient to use the disilane gaswhen the control oxide film 108 is formed immediately after the lightlyphosphorous doped silicon film 106 is formed.

[0062] Next, a control gate 110 is formed over the control oxide film108 as shown in FIG. 3E. In one embodiment, the control gate 110 is aheavily doped polysilicon film. The control gate 110 can be formed usingmethods to form a heavily doped polysilicon film. In one embodiment, thecontrol gate 110 is formed using the method 400 described above in FIG.4. In this embodiment, the phosphorous source gas or the dilutedphosphorous source gas to be introduced into the chamber 12 is increasedso as to form a film that is heavily doped with phosphorous.

[0063] Next, conventional etching methods such as photolithography andreactive ion etching processes can be used to form the structure shownin FIG. 3F. In one embodiment, FIG. 3F illustrates a film stack that isused to form a device such as a FLASH memory device.

[0064] Next, a dielectric film 112 such as silicon dioxide is deposited(blanket/conformal deposition) over the structure as shown in FIG. 3G. Aconventional method such as anisotropic reactive ion etching is used toetch the dielectric film 112 to form the sidewalls 112A and 112B asshown in FIG. 3H. Additionally, source and drain regions 114 can beformed using conventional method to give the final structure of theFLASH memory device (e.g., a FLASH memory device) as illustrated in FIG.3H.

[0065] In one embodiment the various films discussed above are formed insitu, in one deposition chamber. There is no need to change temperaturefor the formation of the different films for a the semiconductor device.Not having the need to change the temperature between depositions thedifferent films is extremely useful when the films are formed in aresistively heated single wafer deposition where controlling thetemperature is more complicated. Further, not needing to change thetemperature between depositions of different films allows fastfabrication of the semiconductor device.

[0066] In another embodiment, the various films described above areformed in different chambers that are arranged into a cluster tool. FIG.6 illustrates an exemplary cluster tool 1100 that includes severalprocessing chambers. For example, the cluster tool 1100 includes asilicon oxide deposition chamber 1102, an annealing chamber 1104, asilicon deposition chamber 1105, and a silicon oxynitride depositionchamber 1106. In one embodiment, each of the silicon oxide depositionchamber 1102, the silicon deposition chamber 1105, and the siliconoxynitride deposition chamber 1106 is a reaction chamber like thechamber 12 described above.

[0067] The cluster tool 1100 also includes a transfer chamber 1108having a wafer handler 1109 (e.g., a robot assembly), which includes awafer clip 1112 for handling a wafer (or a substrate) that is to bedeposited into one of the chambers mentioned above. The wafer clip 1112can be the transfer blade 70 described above in FIG. 2. The transferchamber 1108 is further coupled to a load lock system 1110, which storesthe substrates to be processed. In one embodiment, the wafer handler1109 removes a substrate from the load lock system 1110 and places thesubstrate into an appropriate chamber depending on a process protocol.The wafer handler 1109 also removes a substrate from the chamber oncethe processing is completed and moves the substrate to the nextprocessing chamber or into the load lock system 1110.

[0068] The transfer chamber 1108 is typically set at a reduced pressureas compared to the atmospheric condition. In one embodiment, thetransfer chamber 1108 can also be set at a pressure close to the processpressure that the chambers will be operating at. In another embodiment,the cluster tool 1100 is also set at a pressure that once the wafers arein the load lock system 1110, the loading of other substrates into otherchambers does not impact the operating conditions inside each chamber.When multiple processes are involved, the wafer handler 1109 is used tomove the substrate from one chamber to the next chamber for eachprocess.

[0069] In one embodiment, to deposit a film such as the lightlyphosphorous doped silicon film 106 discussed above, the wafer handler1109 removes a substrate from the load lock 1110 and places thesubstrate in the silicon deposition chamber 1105. The film is thenformed using, for example, the method 400 discussed above in FIG. 4.Once the film is formed, the wafer handler 1109 removes the substratefrom the chamber 1105. In another embodiment, the wafer handler 1109 mayplace the substrate into the chamber 1104 for annealing.

[0070] The exemplary embodiments can be used to form as many films on asubstrate as necessary. For example, the reactant and the doping gasescan be varied depending on the composition of the films to be formed.Thus, the exemplary embodiments above can be repeated as often asnecessary to form as many films as needed. Furthermore, multiple filmscan be formed simultaneously on multiple substrates using the clustertool 1100.

[0071] In another embodiment, the system 10 shown in FIG. 1, the system10 includes the processor/controller 64 and the memory 66, such as ahard disk drive. The processor/controller 64 may include a single board(SBC) analog and digital input/output boards, interface boards andstepper motor controller board. The processor/controller 64 controls allactivity of the system 10. The system controller executes system controlsoftware, which is a computer program stored in a computer readablemedium such as the memory 66. The memory 66 can be stored in a harddisk, a floppy disk, a compact disc ROM (CD-ROM), a digital video disc(DVD-ROM), a magnetic optical disk, or any other types of media suitablefor storing electronic instructions. The computer program includes setsof instructions that dictate the timing, mixture of gases, chamberpressure, heater temperature, power supply, susceptor position, andother parameters of the film deposition processes of the presentinvention. The computer program code can be written in any conventionalcomputer readable programming language such as 68000 assembly language,C, C++, Pascal, Fortran, or others. Subroutines for carrying out processgas mixing, pressure control, and heater control are stored within thememory 66. Also stored in the memory 66 are process parameters such asprocess gas flow rates and compositions, temperatures, and pressuresnecessary to form the films of the exemplary embodiments.

[0072] Thus, according to an exemplary embodiment of the presentinvention, instructions for process parameters for forming the siliconcomprising films are stored in the memory 66. In another exemplaryembodiment, the instructions provide for when and how much of thereactant gases (e.g., the disilane gas, and the phosphorous source gas)are to be introduced into the chamber 12. The instructions also providefor the flow ratios of the reactant gases. Further yet, the instructionsalso provide how much, how hot, and when to heat the chamber 12 or thesusceptor 16 in the chamber 12. The instructions also provide for thecontrolling of the pressure of the chamber 12. The instructions alsoprovide for independent control and variation of the flow rates of eachof the reactant gases and the dilution/carrier gas that are introducedinto the chamber 12.

[0073] In another exemplary embodiment, the cluster tool 1100 of FIG. 6also includes a processor/controller 64 and a memory 66 (not shown inFIG. 6) similar to that included in the system 10 described above. Inaddition to the functions of the instructions as described for thesystem 10, the instructions here further provide for the operation ofmoving the substrate(s) in and out of any particular chamber in thecluster tool 1100 for processing and other operation pertaining tooperating the cluster tool 1100.

[0074] The instructions thus provide or control for most if not all ofthe operations of the deposition processes for the films in the system10 or in the cluster tool 1100.

[0075] While certain exemplary embodiments have been described and shownin the accompanying drawings, it is to be understood that suchembodiments are merely illustrative and not restrictive of the currentinvention, and that this invention is not restricted to the specificconstructions and arrangements shown and described since modificationsmay occur to those ordinarily skilled in the art.

What is claimed:
 1. A method of forming a lightly phosphorous dopedsilicon film comprising: providing a substrate; forming a lightlyphosphorous doped silicon film on said substrate using a process gasmixture comprising a phosphorous source gas and a disilane gas whereinsaid phosphorous source gas and said disilane gas have a flow ratio lessthan 1:100, and wherein said lightly phosphorous doped silicon film hasa doping concentration less than 1×10²⁰ atoms/cm³.
 2. A method offorming a lightly phosphorous doped silicon film comprising: placing asubstrate in a single-wafer deposition chamber; introducing aphosphorous source gas and a disilane gas into said single-waferdeposition chamber, said wherein said phosphorous source gas and saiddisilane gas have a first flow ratio less than 1:100; and thermallydecomposing said disilane gas and said phosphorous source gas at apressure ranging from about 30 Torr to 350 Torr to form said lightlyphosphorous doped silicon film which has a phosphorous dopingconcentration less than 1×10²⁰ atoms/cm³.
 3. A method as in claim 2further comprises mixing said disilane gas with a dilution gas prior tointroducing said disilane gas into said single-wafer deposition chamber.4. A method as in claim 2 further comprising: diluting said phosphoroussource gas with a dilution gas to form a diluted phosphorous source gaswherein said prior to introducing said phosphorous source gas into saidsingle-wafer deposition chamber.
 5. A method as in claim 4 wherein saidphosphorous source gas contained in said diluted phosphorous source gashas a concentration between 0.1% and 10%.
 6. A method as in claim 5wherein said diluted phosphorous source gas has a concentration of about1% and wherein said diluted phosphorous source gas and said disilane gasand has a second flow ratio between 1:10 and 15:10.
 7. A method as inclaim 6 further comprises varying said second flow ratio to vary saidphosphorous doping concentration.
 8. A method as in claim 6 furthercomprising: introducing said disilane gas at a disilane gas flow rate;and introducing said diluted phosphorous source gas at a phosphorous gasflow rate.
 9. A method as in claim 8 further comprising: controllingsaid second flow ratio by varying said phosphorous gas flow rate andsaid disilane gas flow rate.
 10. A method as in claim 2 furthercomprises maintaining said deposition chamber in a process temperatureranging between 500° C. to 650° C.
 11. A method as in claim 2 whereinsaid single-wafer deposition chamber is a resistively heatedsingle-wafer deposition chamber.
 12. A method as in claim 2 furthercomprises annealing said substrate using a thermal annealing process.13. A method as in claim 2 further comprises forming said lightlyphosphorous doped silicon film at a deposition rate ranging from 1000Å/min to about 3000 Å/min.
 14. A method as in claim 2 wherein saidphosphorous source gas is phosphine (PH₃)
 15. A method of forming asemiconductor device comprising: placing a substrate in a single-waferdeposition chamber; maintaining a process temperature between 500° C.and 650° C. and a process pressure between 30 and 350 Torr; introducinga phosphorous source gas and a disilane gas into said single-waferdeposition chamber, said phosphorous source gas and said disilane sourcegas have a flow ratio less than 1:100; thermally decomposing saiddisilane gas and said phosphorous source gas in said single-waferdeposition chamber using a thermal energy source to form a lightlyphosphorous doped silicon film above said substrate, said lightlyphosphorous doped silicon film has a phosphorous doping concentrationless than 1×10²⁰ atoms/cm³; cutting off said phosphorous source gaswhile introducing an oxidation source gas into said single-waferdeposition chamber; and thermally decomposing said disilane gas and saidoxidation source gas using said thermal energy source to form a siliconoxide film above said lightly phosphorous doped silicon film.
 16. Amethod as in claim 15 further comprising: cutting off said oxidationsource gas while re-introducing said phosphorous source gas into saidsingle-wafer deposition chamber; and thermally decomposing said disilanegas and said phosphorous gas in said single-wafer deposition chamberusing said thermal energy source to form a doped phosphorous siliconfilm above said silicon oxide film wherein said doped phosphoroussilicon film has a higher dopant concentration than said lightlyphosphorous doped silicon film.
 17. A substrate processing systemincluding: a susceptor, located within a single-wafer depositionchamber, said susceptor to hold a substrate during a substrateprocessing; a gas supply apparatus for introducing a reactant gasmixture into said single-wafer deposition chamber to deposit lightlyphosphorous doped silicon film over said substrate, said reactant gasmixture comprising a disilane gas and a phosphorous source gas; acontroller for controlling said gas supply apparatus; and a memorydevice coupling to said controller, said memory device comprising acomputer-readable medium having a computer readable program embodiedtherein for directing operation of said substrate processing system,said computer-readable program including instructions for controllingsaid gas supply apparatus to introduce said reactant gas mixture, formaintaining a process temperature between 500° C. and 650° C., formaintaining a process pressure between 30 Torr and 350 Torr, and forcontrolling a flow ratio for said reactant gas mixture.
 18. A substrateprocessing system as in claim 17 wherein said instructions are furtherfor diluting said phosphorous source gas with a dilution gas to form adiluted phosphorous source gas that has a phosphorous concentrationbetween 0.1% and 10% before said reactant gas mixture is introduced intosaid single-wafer deposition chamber.
 19. A substrate processing systemas in claim 17 wherein said instructions are further for diluting saidphosphorous source gas with a dilution gas to form a diluted phosphoroussource gas that has a phosphorous concentration of about 1% before saidreactant gas mixture is introduced into said single-wafer depositionchamber.
 20. A substrate processing system as in claim 19 wherein saidinstructions are further for controlling said flow ratio of said dilutedphosphorous source gas and said disilane gas to be between 1:10 and15:10, said phosphorous source gas to said disilane gas, respectively.21. A substrate processing system as in claim 17 wherein saidinstructions are further for controlling a phosphorous dopingconcentration in said lightly phosphorous doped silicon film and forvarying said flow ratio to vary said phosphorous doping concentration.22. A substrate processing system as in claim 17 wherein saidinstructions are further for controlling said a disilane gas flow ratefor said disilane gas and for controlling a phosphorous gas flow ratefor said diluted phosphorous source gas.